Abstract
There are several reported preparations of the purely synthetic quinones napthazarin (5,8-dihydroxy-1,4-naptho-quinone) and 2-methylnapthazarin. These were investigated with a view to obtaining these compounds on a large scale (ca, 100g.). No reported preparation proved suitable for upscaling, and the various reasons for this are given. Two new methods were attempted for the preparation of napthazarin, also without success; one of these led to a novel bisendo-methyleneanthracene. One method for the preparation of napthazarin, involving chromium trioxide oxidation of a butadiene adduct, was found to give various significant byproducts according to reaction conditions. These were identified and the mechanism leading to their formation is discussed. One such byproduct is a molecular mixture of novel type. With methylnapthazarin an analagous preparation also led to a byproduct, identified as another molecular mixture of different type. Attempts were made to prepare 2-formylnapthazarin from napthazarin and from 2-methylnapthazarin. No success was achieved with direct substitution, and although the previously unknown 2-bromomethylnapthazarin diacetate was obtained, the reactivity of the halogen was such that unwanted side reactions were found to occur very readily. A derivative of unknown structure was obtained from 2-bromomethyl-napthazarin diacetate. Attempts were also made to prepare 2-acetonapthazarin from napthazarin, from 2-aceto-p-benzoquinone, and from quinacetophenone. Again, the desired compound was not obtained. In the Fries rearrangement of napthazarin derivatives, a symmetrical napthofuran, 5,8-dihydroxy-1,3-dimethyhfaaptho [2,3-c]-furan-4,9-quinone, has been obtained and its chemistry appraised. The reaction conditions have been found capable of inducing similar furan ring formation in diethyl a,B-diacetosuccinate. Several partially acetylated napthazarins were obtained. Nuclear magnetic resonance data were obtained for most compounds available (solubility permitting) and for some model compounds. The structure of napthazarin and of substituted napthazarins is discussed in the light of the n.m.r. spectra, and the extent to which n.m.r. data can help in structure assignment in this series is considered.